Truncate density curve in ggplot

[Jens Stevens]

Consider the following example:
ggplot(mtcars)+
  geom_point(aes(y=mpg, x=wt,col=factor(cyl)))+
  geom_density(aes(x=wt,y=..scaled..*30,col=factor(cyl)))

Is there a way to truncate a density curve in ggplot so that it does not extend past the limits of the data? This is most relevant when multiple density curves are present, and refer to different subsets of the data. For instance, eliminate the right tail of the red curve in the example above, and instead immediately drop the density to zero. In the case that I am applying this example to, the data is for an entire population rather than a sample, so having a non-zero density estimate beyond the limits of the data is unrealistic.

Cheers
Jens

[Noam Ross]

Yes, the argument trim=TRUE does exactly this:

ggplot(mtcars)+
  geom_point(aes(y=mpg, x=wt,col=factor(cyl)))+
  geom_density(aes(x=wt,y=..scaled..*30,col=factor(cyl)), trim=TRUE)

This is documented in ?stat_density.

​

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